The present invention relates to the field of data transmission and storage systems and particularly, to redundant data transmission and storage systems suitable for use where high reliability is required such as in telephone message metering systems.
Message metering equipment is employed for recording information resulting from toll, long distance and other types of telephone service. Such equipment requires the ability to detect, transmit and store information to enable usage-sensitive charging of subscribers. Local service by subscribers has generally been on a non-usage-sensitive basis employing equipment which has not been readily adapted to reliable metering on a usage-sensitive basis. With the advent of new types of local telephone usage such as credit-card checking, time-sharing data transmission, and burglary prevention, a need for reliably detecting, transmitting and storing information concerning the nature of local usage has become important.
While the use of redundancy is well-known for improving the reliability of any data transmission and storage system, prior art redundancy techniques have not provided sufficient capability for insuring the reliability and economy of information transmitted and stored in connection with the metering of telephone circuitry.